Diaphragm for loud speakers



Feb. 23, 1932.

A. v. BEDFORD 1,846,937

DIAPHRAGM FOR LOUD SPEAKERS Filed May 9. 1950 Aida Bedford,

a jmwaw His Attorhqg.

Patented Feb. 23, 1932 UNlTED STATES PATENT OFFICE 'ALDA V. BEDFORD, OFSCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC OOMPANY, ACORPORATION OF NEW YORK DIAPHRAGM FOR LOUDSPEAKERS Application filed Kay9, 1980. Serial No. 451,172.

of sound over a wide range of frequency.

Difiiculties have been encountered hereto-v fore in the use of largediameter diaphragms of the cone type arranged to be driven as aunit dueto the tendency of portions of the diaphragm to respond to vibrationscorresponding to the natural vibration period of such portions and toaffect adversely the vibration of portions adjacent thereto. Inaccordance with the present invention these difficult-ies are avoided bythe provision of a multiple diaphragm structure which comprises aplurality of conical sections, adjacent sections being coupled by amember or medium which is essentially dampin in nature. Driving force isapplied preferably to that one of the conical sections which is of thesmallest effective diameter and the force is thence transmitted tosuccessive sections through coupling members constituted by the dampingmembers or medium and interposed between adjacent sections.

My invention will be better understood by reference to the followingdescription when 'considered in connection with the accompanyiugdrawings and its scope will be pointed out in the appended claims.

Referring to the drawings, Figs. 1 and 2 are sectional and plan viewsrespectively of a sound producing device such as a loud speakercomprising a diaphragm embodying the invention, and Fig. 3 is a diagramillustrating the operation of the diaphragm.

In Figs. 1 and 2 is illustrated a sound producing device or loud speakercomprising a cone diaphragm connected at its outer edge to a ring 11 ofyielding material such as leather clamped between mounting rings 12 andnear its apex to a magnet pole 13- by means of a. spider member'lel andstud 15.

The diaphragm is driven by a coil 16 connected thereto near the apexthereof and arranged to vibrate in the space between the magnet poles13. The diaphragm is divided into a plurality of sections, as cone 17'and frustrums of cones 18 and 19. In accordance with the invention thesesections are coupled at their adjacent edges by members 20, 21 whichoperate as damping elements between the sections. In the presentembodiment of the invention.,-20 and 21 are ring shaped members cementedor otherwise fastened to adj acent sections of the diaphragm and formedof or comprising a material of high viscosity or one having a highdamping coefficient and which may at the same time be elastic, such asflexible succinate resin.

The operation of the multiple cone diaphragm comprising the couplingmembers formed of dumping material as above described will best heunderstood by reference to the electrical diagram illustrated in Fig. 3.In this figure inductances Ms and M1 correspond rcspectively to the massof adjacent diaphragm sections, for example to that of cone 17 and of"conical section 18, and resistance R to the damping coupling constant ofthe member 20. whichconnects these sections. Further, the "oltage Ecorresponds to the force applied to the diaphragm and the resultingcurrent in Ms and M1 corresponds to motion of adjacent diaphragmsections, as 17 and 18. Assuming that the constants of the circuit shownin Fig. 3 are such that at a given intermediate frequency the impedanceof M1 is equal to R, then it will be seen that for low frequencies, orfrequencies considerably lessthan the given intermediate frequency,substantially the 'same current will flow in Me and M1. Since current inM8 and M1 corresponds to motion of diaphragm sections 17 and 18,therefore, if driving force of low frequency is applied to the diaphragm10 the adjacent conical sect-ions 17 and 18 partake of thesame motion,or move substantially as one. At high frequencies in' the circuit ofFig. however, R will act as a shunt to M1 due to the greater impedanceof this branch of the circuit at high frequencies and therefore thecurrent flowing through Ms will be greater than that flowing through M1.For the corresponding case of the diaphragm, if driving force of highfrequency is applied to the diaphragm the motion of the smaller conicalsection 17 represented by Ms, will be greater'than that of section 18,represented by M1. At high frequencies, therefore, section 17 willvibratestrongly, but owing to the damping action of coupling member 20the larger conical section 18 will not vibrate appreciably. 7

It will be seen from the above description that the damping membersforming the coupling means between the diaphragm sections so operatethat at low fre uencies the force impressed on the section 0 smallestmass is transmitted to the Whole diaphragm, and as the frequency of theimpressed force rises phragm comprisin a plurality of conical sectionsof different e ective diameters, coupling means for said sectionscomprising members having a high damping coefficient, and meansconnected. to the conical section of smallest effective diameter foractuating said diaphragm. v I e I In Witness whereof, I have hereto handthis 8th day of May, 1930.

ALDA V. BEDFORD.

set my fewer sections respond, until, at high fre quencies, only thesection of smallest diameter responds. By reason of this action of thecoupling means it is possible to prevent any section of the diaphragmfrom breaking up and vibrating appreciably at frequencies correspondingto natural vibration periods of portions of the sections, since. thesection of smallest area may be constructed of such stiffness as'tovibrate only as a single unit even at high frequencies, and since thesuccessively larger sections may be sufficiently stifl' to vibrate assingle units only at those frequencies low enough for each section toreceive appreciable driving force through the damping coupling. j

Further, since in the diaphragm described herein, the sound generatingareas ma be of relatively small diameter compare to a sound Wave lengtheven at very high frequencies, a loud speaker incorporating a diaphragmin accordance with the invention approximates the condition of a pointsource of sound, thus tending to generate a spherical sound wave and tosimplify the interference pattern.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A diaphragm comprising a plurality of sections of successively largerarea, and coupling means for said sections comprising clamping membersconnected to adjacent sec- 7 tions.

2. In a diaphragm, a plurality ,of conical one of said sections, saidcoupling means being arranged to transmit said force from one of saidsections to'the others thereof in succession.

5. In a sound producing device, a dia-

